Epoxy resin compositions for the sealing of optical semiconductor elements often employ liquid epoxy compounds each having an alicyclic skeleton that is satisfactorily transparent and thermally stable. Such epoxy compounds are typified by CELLOXIDE 2021 [3,4-epoxycyclohexylmethyl(3,4-epoxy)cyclohexanecarboxylate], CELLOXIDE 2081 [an adduct of 3,4-epoxycyclohexylmethyl(3,4-epoxy)cyclohexanecarboxylate with ε-caprolactone dimer], and CELLOXIDE 3000 (1,2,8,9-diepoxylimonene) each supplied by Daicel Chemical Industries Ltd.
Alicyclic epoxy compounds having a 3,4-epoxycyclohexylmethyl(3,4-epoxy)cyclohexanecarboxylate structure, represented by CELLOXIDE 2021, can be cured to give cured articles having excellent thermal stability and satisfactory transparency, and are thereby used as resins for sealing or encapsulating optical semiconductors such as LEDs. However, the alicyclic epoxy compounds such as CELLOXIDE 2021, when used alone, may exhibit insufficient heat-cycle endurance to suffer from cracking, and thereby cause product electronic components to have insufficient reliability.
Exemplary customary proposals to improve properties of epoxy resins typically for improving impact strength or for suppressing the occurrence of cracking are as follows. Japanese Unexamined Patent Application Publication (JP-A) No. H09-255764 discloses an epoxy resin composition which includes a hydrogenated bisphenol-A diglycidyl ether and which is used for sealing an optical semiconductor. JP-A No. H10-156952 discloses a stereolithographic resin composition using an alicyclic epoxy compound. JP-A No. 2000-63485 discloses a curable composition for buildup, containing a specific alicyclic epoxy compound and a polyepoxy compound having a polyhydric phenol (polyphenol) skeleton. JP-A No. H09-71636 describes an active-energy-ray-curable composition using an alicyclic epoxy compound. PCT International Publication Number WO2006/064736 discloses a thermosetting resin composition including a polyol oligomer.